The star of the haul was an extremely rare coin known as a "Tricentennial Royal" minted in 1715. It had been underwater since a fleet of Spanish ships foundered during a hurricane along Florida's Treasure Coast 300 years ago, Schmitt said.

"These things were known as presentation pieces not meant to be circulated as currency," Schmitt said.

That coin alone is worth about $500,000, according to Schmitt.

For the past two summers, the Schmitts have made national news thanks to their discoveries from the fleet of Spanish ships that wrecked in July 1715.

In 2013, the family found several pieces of a solid gold chain — more than 60 feet in all — and last year Schmitt found the back portion of a handcrafted gold-filigree pyx, a vessel used to hold the Eucharist during the Christian observance of Holy Communion.

Brent Brisben is the co-founder of 1715 Fleet - Queens Jewels LLC, the company that owns the rights to the wreckage where the family found the gold. Brisben says the artifacts date from a 1715 maritime tragedy in which 11 Spain-bound galleons were lost during a hurricane.

He says the items recovered include 52 gold coins and 40 feet of ornate gold chain. The rare coin, Tricentennial Royal, was destined for the king of Spain.